I wanted to calculate Thermodynamic parameters such as Gibbs Free energy, Enthalpy change and Entropy change using Curtis et al explained as this link: https://gaussian.com/wp-content/uploads/dl/thermo.pdf When calculating these parameters at standard temperature I use this table values for individual atoms like C, H etc (table in page 16 in the above pdf) I want to know when I calculate above parameters at high temperature will these table values remain the same or different? If it differs how to find/calculate them? TIA
No, of course they are both subject to change, otherwise G wouldn't change, either. You can calculate the difference by integrating over the heat capacity cp for H and the ratio cp/T for S. However, I am not sure you will find proper experimental values for cp for all these species in gas.
Elsewhere at this forum, I have discussed the apparent possiblity of high temperature formation of hydrogen cyanide (HCN) after CHi radicals (i = 1, 2, 3) reacting with (gaseous) nitrogen species, possibly involving heterogeneous catalysis:
https://www.researchgate.net/post/formation-of-cyanide-in-vacuum-sintering-in-high-temps-like-2000-C-with-nitrogen-atmosphere
I have also discussed the case of high temperature dissociation of H2 to atomic H for a (previous) gas misture of H2 and He ― while specifically adressing its heat capacity ratio (γ = Cp/Cv): https://www.researchgate.net/post/how_can_we_calculate_gamma_specific_heat_ratio_for_real_gas_chemical_non-equili/1
It is not clear to me what the table contains. Are the entries in the 1st column enthalpies of formation for atoms (i.e., enthalpy of dissociation for H2, or enthalpy of sublimation for Li) in the ideal-gas state? If yes, you may set Cp =2.5 R.
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